Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/24—Crosslinking, e.g. vulcanising, of macromolecules
  • C08J3/247—Heating methods

Definitions

• This invention relates to a process for curing vulcanizable materials by means of a liquid heat transmitter, in particular a process for the thermal vulcanization of thermosetting resins or vulcanizable elastomers or copolymers.
• the present invention especially relates to a process for carrying out the hot cure of thermosetting resins or vulcanizable elastomers, based on the use of a specific product, in the liquid state, to transmit heat to the material that has to be cured, in order to heat said material to a temperature that has been pre-established for the curing process.
• thermosetting resins such as epoxy resins, unsaturated polyesters, polyurethane and polybutadiene resins, by using, as liquid medium, glycerin, ethylene glycol and wax or petroleum resins (paraffins), which are liquid at the processing temperature.
• liquid transmitters mentioned above do not provide the necessary high chemical inertia as to the vulcanizable material, in order to obtain high quality manufactures.
• thermosetting resins make use of a saturated vapor coming from a liquid kept at the boiling temperature, as heating medium. See in this connection U.S. Patent No. US-A-4,517,356.
• This method although it allows curing at a perfectly controlled and homogeneous temperature in a very short time and with good results, presents, however, the drawback that the operating temperature is determined by the boiling point of the liquid which has been used, and should it be necessary to change this temperature to adjust it to a different kind of resin or to a different process, the liquid has to be changed as well.
• the present invention provides a process for curing vulcanizable materials, in particular thermosetting resins or vulcanizable elastomers or copolymers, comprising contacting an article to be cured with a process liquid at a pre-established temperature for a sufficient time in order to obtain complete vulcanization, characterized in that said liquid is a perfluoropolyether.
• the process according to the present invention allows the most convenient conditions of temperature to be selected, using the same liquid.
• the loss of the liquid product due to evaporation may be very low, when a liquid is selected having a low vapor tension.
• Another advantage of the process according to the present invention is that it allows a multi-step curing process to be carried out, with different vulcanization temperatures in each step, by using the same liquid in all the steps; in the vapor phase, on the contrary, use has to be made in each step of a different kind of liquid having a different boiling point, corresponding to the temperature conditions of each step, but in practice the possibility of changing the thermal profile of each step is limited by the nature of the system.
• a vapor phase system involves the pollution of the new liquid with the old one, when the liquids change from one step to the other.
• the process of the present invention consists essentially in bringing into contact the article to be cured with the process liquid kept at a pre-established temperature and for a period of time sufficient to obtain the complete vulcanization.
• the contact between the process liquid and the material to be cured can be obtained in the most simple way, by dipping the article into a bath containing the liquid at the desired temperature. Alternatively it can be carried out by means of a customary spray system or by dipping into a film of liquid.
• liquid products used as heat transmitters in the process according to the invention belong to the class of perfluoropolyethers of neutral kind, namely without reactive terminals, having perfluoroalkyl terminals and very low vapor tension under the process conditions.
• Perfluoropolyethers having viscosity at 20°C ranging from 10 to 2500 Cst may be suitably used in the present invention.
• the perfluoropolyethers preferably used in the present invention have a perfluoropolyethereal structure, comprising structural units of the following kinds:
• perfluoropolyethers containing the units mentioned above are known and are selected preferably among the following classes:
• perfluoropolyethers exhibit a high degree of the following properties: - inflammability; - stability at high temperatures; - good coefficient of heat transfer; - chemical inertia; - lack of solid residue; - good compatibility with the materials used in electronic apparatuses; - low viscosity at the utilization temperatures; - low surface tension (good wettability and drainage); - high specific heat.
• the characteristic that first differentiates the liquid product utilized in the present invention from those of the prior art is high compatibility of such products with all the thermosetting resins, such as epoxy, polyurethane, polyester, acrylic, polybutadiene, polyimide resins.
• the compatibility is based substantially on the following properties: - lack of any chemical reaction with the resin before, during and after curing; - no (or very low) capability of dissolving the resin and lack of absorption and/or of gelling phenomena before, during or after curing.
• Another advantageous characteristic of the perfluoropolyesters mentioned hereinbefore for use in the present invention is their lack of toxicity, smell or irritant properties.
• the curing process may be carried out in combination, simultaneously or in sequence, with electronic radiation, U.V. radiation, microwaves or supersonants; these different energetic sources may be used singly or together.
• An advantage of the use of U.V. radiation in combination with the vulcanization in the liquid phase of the present invention is that the harmful effects of atmospheric oxygen are eliminated, inhibiting strongly induced radical polymerization.
• the excess energy coming from the microwaves may be dissipated by the fluid, in order to improve the thermal control of the system.
• the vulcanization in the liquid phase allows the rate of the surface vulcanization to be controlled or to be increased in order to provide a better, non-sticky surface, cured outside, but allowing at the same time preliminary handling before the complete vulcanization.
• the complete vulcanization may be carried out by using a curing agent in the liquid phase, optionally in the presence of the energetic sources mentioned hereinbefore.
• the contact between the heating liquid and the article to be heated may be carried out in several ways, for instance. - by dipping into the liquid, - by spraying of the liquid, - by passing through a wave of liquid.
• Such polymeric film can be used in order to restrain volume increase taking place during the vulcanization and/or gas elimination during the starting vulcanization step and therefore to act as a continuous heat transmitter.
• the wrapping may be carried out according to the techniques of vacuum wrapping or shrink wrapping.
• the protective film can be also used to avoid the inclusion of the heating liquid in highly delicate manufactures such as, for instance, printed circuits comprising electronic components, which can be sensitive to the liquid.
• the articles subjected to the process according to the invention can be washed afterwards with a specific solvent in order to remove the residual heating liquid.
• Suitable solvents are fluorinated or chlorofluorinated hydrocarbons such as Algofrene® 113.
• thermosetting resins As practical examples of the application of the present invention there can be mentioned the vulcanization of parts of epoxy resins present in printed circuits, coatings consisting of thermosetting reins, and couplings achieved by using thermosetting resins as binders.
• the resin that can be cured according to the present invention is any vulcanizable material which can be cured by thermal treatment.
• vulcanizable material examples include thermosetting resins, thermally vulcanizable thermoplastic compositions, for instance PVC containing plastisol, elastomeric compositions such as EPR and EPDM, and cross linkable polymers such as polyolefins XLPE, CPE, CSM.
• the temperature control together with the high speed of heat transmission may allow a quick and effective vulcanization at lower temperatures than those used previously in the prior art.
• the mixture was pre-cross-linked at 100°C during 1 hour, after which it was cross-linked at 165°C according to two methods:
• perfluoropolyether exhibits absolute chemical inertia and compatibility towards polymeric materials.
• the mixture was pre-cross-linked at 100°C during 1 hour, after which it was cross-linked at 190°C and 215°C, according to methods A and B described in Example 1.
• Two pressure sensitive adhesive tapes having a thickness of about 0.15 mm were stuck parallelly at a distance of 5 mm on polyester supports having a thickness of 0.2 mm, coated with a silica layer having a thickness of 0.25 mm.
• a two component Epotek®H20 resin (containing Ag in the form of finely dispersed powder) was spread between the two tapes in order to form a deinite track.
• the resin was pre-treated at 50°C over 30 minutes, before being applied on a board.
• the adhesive tapes were removed and the resin was cross-linked both in an oven and in a liquid phase as specified hereinbefore.
• the volumetric resistivity was measured by Thiedig Milli-TO.2 method in a cell purpose built according to UNI 5608 method (measuring method type 4 electrode Kelvin), after having measured carefully the track size by means of a digital micrometer and a graduated optical visual apparatus.
• volumetric resistivity was measured according to the method indicated in example 3.
• Example 3 was repeated, by heating the boards either in a heating plate oven or by dipping in perfluoropolyether phase at 175°C. The results are set forth in Table 5.
• the mix was extruded in shapes having a rectangular section of 35x1.5 mm., from which specimens were obtained, being about 10 cm in length.
• the specimens were cross-linked by dipping into a bath containing Fomblin YR, the characteristics of which are set forth in Example 1.
• the specimens When the reticulation was over, the specimens had a dry, unsticky aspect; moreover they exhibited considerably better surface properties in comparison with those obtained by reticulation at the same temperature in a melted salt bath by percolation in vapor phase. In fact, cured articles were obtained, wherein total lack of bubbles and of surface roughness was noted.
• Dicumyl peroxide (PEROXIMON DC®) as cross linking agent, triallyl cyanurate as co-cross linking agent and an antioxidant (ANOX HB®) were added to a "low density" polythene having melt flow index 2 according to the following formula: PE 100 Parts by weight Dicumyl peroxide 2 Parts by weight T AC 0.5 Parts by weight ANOX 0.5 Parts by weight
• the "compound” was shaped obtaining a specimen having section 10 cm x 10 cm x 2 mm.
• This shaped specimen was dipped into a bath containing FOMBLIN YR the characteristics of which are set forth in example 1.
• the weight loss due to the solvent for a non-cross linked specimen was 37.7% by weight, while the weight loss for the specimen treated according to the present invention was 3.9%. Said value is lower than the value for a cross linked specimen carried out by pressing.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Processes Of Treating Macromolecular Substances (AREA)

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• 1987
  • 1987-04-17 IT IT20167/87A patent/IT1203925B/it active
• 1988
  • 1988-04-13 US US07/180,892 patent/US4874842A/en not_active Expired - Fee Related
  • 1988-04-15 EP EP88303439A patent/EP0287398B1/fr not_active Expired
  • 1988-04-15 DE DE8888303439T patent/DE3863462D1/de not_active Expired - Fee Related
  • 1988-04-16 JP JP63094391A patent/JPS6470534A/ja active Pending

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